The 0.18 is when one UTXO is spent, I think it is not a wallet problem, but a characteristic of the protocol. The 1 ADA you sent was probably from several UTXOs. Here is a quote that might help: "Dust is the term for when small UTxOs gather in a user’s wallet over time. These UTxOs are so small that it costs more in transaction fees than they are worth to send over the network. The distribution of these UTxOs depends upon the underlying coin selection algorithm used by the wallet. " https://emurgo.io/understanding-unspent-transaction-outputs-in-cardano/

It can be, depending on the UTXO structure in your wallet - from which the ADA was sent. Sometimes before sending it, play around with different amounts 1 or 2 or 5 ADA or more, the transaction fee can differ - depending how many UTXOs are consumed. So you can set up the transaction with sligthly different amounts before sending it, check the transaction fee before clicking send - it might be a bit lower or higher...